It is very important to be able to uniformly disperse an organic compound in water since the dispersion can be industrially handled as an aqueous solution. Practically, there are dispersions of latex polymers, waxes, etc., and various kinds of emulsions. In particular, recently, in the field of manufacture of information recording papers such as heat-sensitive recording papers, etc., it has been required to disperse organic compounds having a low melting point in water uniformly and in a fine particulate state. More particularly, in the case of heat-sensitive recording papers, it is an important technical point to uniformly disperse fine particles of organic compounds since the particle size of the dispersion influences important properties such as the sensitivity, etc., of the recording material, as described in British Patent 2,085,178. Thus, various attempts such as the use of a media mill have been provided as described in JP-A-58-69089 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"). However, in this case, there is a problem that when the temperature of the dispersion system necessary for obtaining a dispersion of desired fine particles is greatly increased, a stable dispersion is not obtained.
This tendency becomes more severe as the melting point of an organic compound being dispersed is lowered.
On the other hand, a recording material using an electron-donating dye precursor (hereinafter referred to as a color former) and an electron-accepting compound (hereinafter referred to as a color developer) is well known as pressure-sensitive recording papers, heat-sensitive recording papers, light- and pressure-sensitive recording papers, and electro-heat-sensitive recording papers. These recording papers are described in detail, for example, in British Patent 2,140,449, U.S. Pat. No(s). 4,480,052 and 4,436,920, JP-B-60-23922 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), JP-A-57-179836, JP-A-60-123556 and JP-A- 60-123557.
A recording material is required to perform so that (1) the color density and the coloring sensitivity are sufficient, (2) fog is not formed, and (3) the storage stability of the colored product after coloring is sufficiently high. However, recording materials completely satisfying the aforesaid requirements have not yet been obtained.
In particular, recently, the range of applications using heat-sensitive recording materials has increased and in various applications of the recording papers, the fastness required for the colored product has increased even more. In such recording materials, the storage stability of colored products under high temperature and high humidity conditions is important.
For improving the aforesaid storage stability, it has been proposed to use a mixture of two or more color formers, as disclosed in JP-B-59-53193. However, when two or more kinds of color formers are used as a mixture thereof, the formation of fog at white portions or background portions increases and the formation of the fog is particularly increased under high temperature and high humidity conditions.
Also, for obtaining a sufficient coloring sensitivity, an attempt has been made to reduce the particle sizes of the color former(s) and color developer, whereby their surface areas thereof are enlarged to increase the reactivities. However, such an attempt also increases the formation of fog in the heat-sensitive recording materials.
For preventing the formation of fog, various attempts have been proposed. For example, an attempt involving protecting at least one of the color former and the color developer with a protective colloid (water-soluble polymer) having a high adsorptive power to restrain the occurrence of reaction between the color former and color developer in the coating composition containing them is disclosed in JP-B-51-29945, JP-A-56-55288, JP-A-55-28805, and JP-A-55-159992, an attempt involving restraining the occurrence of reaction between the color former and color developer in the coating composition by keeping the pH of the coating composition at an alkaline state is disclosed in JP-B-51-28235 and JP-B-55-6077, an attempt involving using a neutral paper as the support for the heat-sensitive recording paper is disclosed in JP-A-55-14281, an attempt involving adding an antifoggant to the coating composition for the heat-sensitive layer is disclosed in JP-B-49-3943 and JP-A-48-101943, and also an attempt involving heat-treating the fine dispersion of the aforesaid two components is disclosed in JP-A-54-98253.
However, many of these attempts are accompanied by the disadvantages that the effects are insufficient, they raise the manufacturing cost, and/or the steps become complicated, and hence these attempts are not always satisfactory for practical purposes.